The Philadelphia Social History Project (PSHO) seeks to deepen our understanding of the micro-level workings and consequences of urbanization and industrialization. To accomplish this task it has converted to machine readable form a vast body of historical information describing the 2.5 million persons who lived in Philadelphia in the years 1850, 1860, 1870 and 1880 as well as their careers, housing, businesses, manufacturing firms, transportation facilities, public and private institutions, and marriage and death records. The PSHP serves as the umbrella organization for an interdisciplinary team of pre- and post-doctoral scholars from sociology, economics, demography and geography, as well as from history. The PSHP covers four research areas. "The Nature of Work" is concerned with how changes in scale, productivity, mechanization and the organization of work shuffled the occupational universe and affected the opportunity structure. "The Uses of Urban Space" focuses on the process of spatial differentiation which gradually transformed Philadelphia from its colonial/commercial character of compactness and heterogeneity in residence, business and industry to its modern/industrial character of decentralized sprawl, sharp segregation in residence, and distinct zones of commerce and industry. "Life-Course Developments" studies the timing and sequencing of consequential individual-level decisions and events by arraying them in "careers," e.g., in jobs, residence, family. "Special Group Experiences" examines Blacks, Irish and Germans; the "Aristocracy of Labor," the emerging industrial elite, the poor, welfare recipients, criminals and women in order to learn how work, migration, social and residential mobility, assimilation, family behavior, fertility and mortality--holding constant the setting of rapid urbanization and industrialization--were mediated by the four major differentiators of experience: race, ethnicity, class and sex.